P. Hubert Mutin

Hybrid materials from organophosphorus coupling molecules

Organophosphorus acids and their derivatives (salts, esters) are quite complementary of organosilicon coupling molecules for the preparation of hybrid organic–inorganic materials, by sol–gel processing or surface modification. Organosilicon compounds are best suited for the anchoring of organic groups to silicon-containing inorganic matrices or supports, such as silica, silicates, silicon carbide, etc., whereas organophosphorus coupling molecules appear well adapted to matrices or supports based on metals or transition metals: oxides, hydroxides, as well as carbonates and phosphates. The different reactivity of organophosphorus coupling molecules leads to different structures and stabilities of the final hybrid materials and may provide decisive advantages in the sol–gel synthesis of homogeneous hybrids, the preparation of surface monolayers or the selective surface modification of nanopatterned supports.

Control of the Composition and Structure of Silicon Oxycarbide and Oxynitride Glasses Derived from Polysiloxane Precursors

The reactions involved in the preparation of silicon oxycarbide and oxynitride glasses by pyrolysis of polysiloxane precursors respectively under argon and ammonia are reviewed. The influence of the composition and structure of the precursor and of these pyrolysis reactions on the pyrolysis yield, the composition, and the structure of the glass is discussed. The free-carbon content of the glass depends on the substituents in the precursor and on the nature of the pyrolysis atmosphere. The composition of the oxynitride or the oxycarbide phase depends on the O/Si ratio of the precursor. The structure of these phases is not directly related to the structure of the precursors, but rather depends on their composition and on the pyrolysis temperature.

Mixed oxides SiO2–ZrO2 and SiO2–TiO2 by a non-hydrolytic sol–gel route

SiO2–ZrO2 and SiO2–TiO2 mixed oxides with various metal contents have been prepared by a non-hydrolytic sol–gel route involving the condensation between chloride and isopropoxide functions at 110 °C. Well condensed, monolithic gels were obtained in one step, without the use of additives. The Si/M ratio of the oxide may be controlled easily by the composition of the starting mixture. The Si/Zr oxides remained amorphous after calcination for 5 h at 600 °C; IR and 29Si NMR spectroscopy showed a large amount of Si–O–Zr bonds, indicating a homogeneous distribution of the components on the atomic scale. The crystallization of tetragonal zirconia took place at higher temperature; the transformation of tetragonal to monoclinic zirconia was strongly retarded and did not take place after 2 h at 1300 °C. The crystallization of zircon (for a sample containing 50 mol% Zr) started at 1500°C and was completed after 20 h at 1500°C. IR spectroscopy indicated the presence of a limited number of Si–O–Ti bonds in all the Si/Ti oxides after calcination for 5 h at 500 °C. The sample within the stable glass region (5 mol% Ti) appeared perfectly homogeneous: it crystallized at 900 °C as single-phase cristobalite oxide, with Ti4+ ions substituting Si4+ ions at random. On the other hand, the precipitation of anatase was observed for the Si/Ti oxides with a high Ti content (20–50 mol% Ti), which are outside the stable glass region. The transformation of anatase to rutile was not observed even after 2 h at 1300 °C.

Bonding-induced thermal conductance enhancement at inorganic heterointerfaces using nanomolecular monolayers

Manipulating interfacial thermal transport is important for many technologies including nanoelectronics, solid-state lighting, energy generation and nanocomposites. Here, we demonstrate the use of a strongly bonding organic nanomolecular monolayer (NML) at model metal/dielectric interfaces to obtain up to a fourfold increase in the interfacial thermal conductance, to values as high as 430 MW m(-2) K(-1) in the copper-silica system. We also show that the approach of using an NML can be implemented to tune the interfacial thermal conductance in other materials systems. Molecular dynamics simulations indicate that the remarkable enhancement we observe is due to strong NML-dielectric and NML-metal bonds that facilitate efficient heat transfer through the NML. Our results underscore the importance of interfacial bond strength as a means to describe and control interfacial thermal transport in a variety of materials systems.

Ionic liquid as plasticizer for europium(III)-doped luminescent poly(methyl methacrylate) films

Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(6)mim][Tf(2)N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C(6)mim][Eu(nta)(4)], [C(6)mim][Eu(tta)(4)], [Eu(tta)(3)(phen)] and [choline](3)[Eu(dpa)(3)], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with beta-diketonate complexes are characterized by a very intense (5)D(0)-->(7)F(2) transition (up to 15 times more intense than the (5)D(0)-->(7)F(1)) transition, whereas a marked feature of the PMMA films doped with [choline](3)[Eu(dpa)(3)] is the long lifetime of the (5)D(0) excited state (1.8 ms).

Preparation of anatase, brookite and rutile at low temperature by non-hydrolytic sol–gel methods

Titania samples prepared by different non-hydrolytic sol–gel methods, mainly based on the etherolysis and alcoholysis of titanium tetrachloride, have been found to differ in both structure and texture. Thus, the reaction of diethyl ether with TiCl4 at 110 °C affords anatase, which begins to convert into rutile only around 1000 °C. The reaction of TiCl4 with ethanol leads to rutile as early as 110 °C, whereas the reaction of tert-butyl alcohol at 110 °C leads to the singular formation of brookite.

Phosphonate monolayers functionalized by silver thiolate species as antibacterial nanocoatings on titanium and stainless steel

Titanium and stainless steel substrates were modified by grafting with mercaptododecylphosphonic acid (MDPA) followed by reaction with silver nitrate (AgNO3), in order to investigate the potential of phosphonate self-assembled monolayers functionalized by silver thiolate species as antibacterial nanocoatings for inorganic biomaterials. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy in grazing-incidence mode, water contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The influence of the surface modification on bacterial adhesion and biofilm growth was investigated in vitro using Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus strains. The stability of the monolayer in blood-mimicking medium was examined. Despite their very low silver content, MDPA + AgNO3 monolayers strongly decreased bacterial adhesion (>99.9% reduction in the number of viable adherent bacteria) and biofilm formation in comparison to the bare substrates.

Materials chemistry communications. Preparation of monolithic metal oxide gels by a non-hydrolytic sol–gel process

Non-hydrolytic condensation between halide and alkoxide metal precursors leads to oxide gels; thus, Al2O3 and TiO2 were successfully synthesized as monolithic gels.

Influence of the nature of the organic precursor on the textural and chemical properties of silsesquioxane materials

The hydrolytic sol-gel polymerization of molecular organosilicon precursors with a rigid geometry C6H4[Si(OMe)3]2-1,4 and C6H3[Si(OMe)3]3-1,3,5 2 was investigated and compared to the results obtained with precursors having a more flexible structure C6H4RR-1,4 [R=R=CH2Si(OMe)3 3; R=R=CH2CH2Si(OMe)3 4]. Compounds 1-4 have been studied in the same conditions. They were hydrolyzed under nucleophilic catalysis (TBAF: tetrabutylammonium fluoride) in MeOH and in THF. The structure of the organic group was found to be a determining parameter for both the physical and chemical properties of the resulting silsesquioxane materials. The molecular precursors 1 and 2 containing a ‘rigid’ organic group led to hydrophilic solids with similar degrees of condensation. In all cases, high specific surface area (370-1018 m2 g1) and poor chemical reactivity towards Cr(CO)6 (11-33) were observed. By contrast, the precursors containing a ‘flexible’ organic group (3 and 4) led to hydrophobic solids; the texture, the degree of condensation and the reactivity towards Cr(CO)6 of these solids strongly depended on the solvent. For instance the solids prepared in MeOH had no significant specific surface area. The solids derived from the most flexible precursor (4) exhibited the highest chemical reactivity. The short range organization of the solid is a function of the geometry of the precursor and the experimental conditions.

Non-hydrolytic synthesis of mesoporous silica-titania catalysts for the mild oxidation of sulfur compounds with hydrogen peroxide.

A SiO(2)-TiO(2) mesoporous xerogel prepared in one-step by a non-hydrolytic route shows excellent performance in the mild oxidation of sulfides, sulfoxides and thiophenes with aqueous solutions of H(2)O(2).